Development of Spin-echo NMR Technique for High-gradient Magnetic Field Measurement

到目前为止，人们一直担心不可能将核磁共振技术应用于高梯度磁场的精确测量，例如加速器中使用的四极磁铁。为了克服磁场梯度带来的困难，我们发展了用于磁场测量的自旋回波核磁共振技术，该技术可以检测自旋回波信号中的自旋进动频率。通过对自旋回波信号检测和自旋回波谱的理论信噪比的模拟研究，预测了在高梯度磁场中观测自旋回波信号的可能性。在一个基于理论研究的实验中，我们使用一个简单的固定频率的自旋回波探测器，在2.35公斤的场强和高达0.55T/m的梯度下清楚地观察到了自旋回波信号。自旋回波信号中恢复的核磁化的进动频率取决于核磁共振样品的大小，但RES…的情况除外更常见的是，180°脉冲的射频频率与由样品中的平均场强确定的核磁共振频率一致。我们在教育部科学研究助学金的支持下，研制了一台用于寻找场强和消除样本量影响的变频自旋回波探测器。此时此刻，我们正处于系统调整的最后阶段。在开发探测器的同时，我们研究了用于现场测量的自旋回波信号的频谱分析方法。将改进的FFT分析应用于自旋回波信号，在2.35 kg处获得了0.45g的分辨率，并从实验上证实了样本量的影响。在探测器调谐完成后，我们将在KEKB/LER弯曲磁体的~15g/cm梯度场中进行长期性能测试。在最后一步中，我们将尝试对KEKB加速器的四极磁铁进行磁场测量，磁场梯度为~10T/m。较少

Until now it has been concerned impossible to apply the NMR technique to the precise measurement of high-gradient magnetic fields such as in quadrupole magnets use in accelerators. To overcome difficulties due to the field gradient, we have developed the spin-echo NMR technique for magnetic field measurement where the spin precession frequency in the spin-echo signal is detected.Simulation studies of spin-echo signal detection and the theoretical signal-to-noise ratio of the spin-echo spectrum predict the possibility of spin-echo signal observation in a high-gradient magnetic field. In an experiment based on theoretical studies, we observed spin-echo signals clearly at a field strength of 2.35kG with a gradient of up to 0.55T/m using a simple fixed frequency spin-echo detector. This result can be scaled to a gradient of 5T/m at 10kG.The precession frequency of the recovered nuclear magnetization appearing in the spin-echo signal depends on the NMR sample size, except in the case of res … More onance where the rf frequency of the 180°-pulse coincides with the NMR frequency determined by the average field strength in the sample. We developed a variable frequency spin-echo detector to search the field strength and to eliminate the sample size effect with the support of a Grant-in-Aid for Scientific Research from the Ministry of Education. At this moment we are in the final stage of system tuning. In parallel with detector development, we studied methods for spectral analysis of the spin-echo signal for the field measurement. Applying an improved FFT analysis to the spin-echo signal, we obtained a resolution of 0.45G for the field measurement at 2.35kG, and we confirmed the sample size effect experimentally. This result indicates that we can realize a resolution smaller than 0.1G without serious difficulties.After completion of detector tuning, we will perform a long term performance test in the gradient field of 〜15G/cm at a KEKB/LER bending magnet. In the final step, we will attempt field measurement of a quadrupole magnet of the KEKB accelerator with 〜10T/m field gradient. Less